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Using XXMIT, XMIT, or L9_XMIT on Momentum, a loss of communications between a PLC Modbus Master and Slave is not detected

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Goals and Symptoms

This Resolution is to inform users of Unity Momentum processors about an issue when using the XXMIT communication function block. The XXMIT, XMIT, and L9_XMIT will not exhibit an error 116 (communications timeout) in the 'Status' output word of the function block if the communications cable is removed between the master and slave device.

Facts and Changes

The XXMIT, XMIT, and L9_XMIT will not exhibit an error 116 (communications timeout) in the 'Status' output word of the function block if the communications cable is removed between the master and slave device.

The normal operating behavior of a broken media between a master and slave device is that an error 116 will be displayed in the STATUS output of the XXMIT function block. In specific versions of Unity, an error 116 will not be observed.

The following table lists these conditions.

XXMIT with Unity Version

Status

Solution

8

Fails – No error 116 displayed

Upgrade to Unity 11
Install - HF1
Install - UnityPro_V110_HF0258202R

8.1

Fails – No error 116 displayed

Upgrade to Unity 11
Install - HF1
Install - UnityPro_V110_HF0258202R

10

Functional– Error 116 is displayed

No action required

11

Fails – No error 116 displayed

Install - HF1
Install - UnityPro_V110_HF0258202R

Solution will be in Unity 11.1, scheduled for August 2016. (original June 2016 release date has changed)

Causes and Fixes

Products affected:

171CBU78090

171CBU98090

171CBU98091

After updating to Unity 11, there are two additional HotFixes that must be installed to fix this issue.